1. Field of the Invention
The present invention relates to fluid leak testers and, more particularly, to an isolator for a leak detector to detect proper operability of the leak detector and the delivery lines in a gasoline dispensing system.
2. Description of the Prior Art
Retail gasoline stations dispense different grades of gasoline and diesel fuel for automotive vehicles. These fuels are stored in respective storage tanks underground and dispensed from respective pumps for the benefit of retail users. A submerged pump is disposed in the storage tank to provide fuel under pressure at the dispenser. It is well known that leaks can and do occur between the output of the storage tank and the input of the dispenser. These leaks may result from destructive forces resulting from settling of the storage tank. Vehicular movement over the ground may cause a shift of the earth and impose sufficient forces to affect the integrity of junctions or unions disposed along the fuel delivery line. Rocks or other hard substances may impinge upon and wear or otherwise dimple the delivery line sufficiently to develop a leak. Sometimes corrosion due to acids or salts will affect the integrity of the delivery line or a seal at a junction.
Because of the long term destructive effects of seepage of fuel in the ground, the Environmental Protection Agency has established requirements which eliminate or at least reduce future ground contamination. To comply with these requirements, as well as to reduce fuel losses and the attendant economic detriments, a device generically known as a leak detector is mounted at the storage tank. This leak detector is disposed between the output of the submerged pump within the storage tank and the input to the line delivering fuel from the storage tank to the dispenser.
Such a leak detector has three operative states. In the relaxed state prior to energization of the submerged pump, a flow into the delivery line at the rate of 1.5 to 3 gpm is permitted. Upon energization of the submerged pump, a poppet valve is partly actuated to limit flow through the leak detector to a rate of 3 gph. Assuming that the delivery line has a leak of less than 3 gph, the pressure within the leak detector will build rapidly (approximately 2 seconds) and the valve will go to the fully open position to permit unimpeded fuel delivery. If there is a leak greater than 3 gph, insufficient pressure will build up to permit full delivery. Alternatively, a leak close to but less than 3 gph will increase the time required to go to the full delivery position.
These leak detectors, for the most part, perform admirably well over long periods of time with limited maintenance. Unfortunately, due to wear and contamination, the leak detector may permit full delivery even though a leak greater than 3 gph may be present. Because fuel is still delivered after an initial hesitation period, the gasoline station operator may not be aware of the existence of a leak. The leak detectors are periodically tested but such testing of a leak detector independently of influence of the delivery system requires removal of the leak detector to a laboratory-like environment. The resulting delays and expenses tend to encourage infrequent testing.